Disc drives for modern desktop computer systems record and reproduce information on a recording medium. The medium generally takes the form of a stack of circular information storage discs having a multiplicity of concentric tracks. Conventional Winchester type disc drives include a disc stack having one or more vertically aligned information storage discs which are journaled about the hub portion of a single spindle assembly. Each disc has at least one associated magnetic head that is adapted to transfer information between the disc and an external system. The heads are typically arranged to move back and forth radially across the disc and a spindle motor assembly is provided to rotate the discs. The movements of the spindle and the magnetic heads cooperate to allow random access to any portion of the disc.
Although disc drives are a relatively old and established technology, consumer demands continuously push for more compact, higher capacity, faster accessing designs. One of the size limiting components in traditional designs has been the spindle motor assembly used to rotate the information storage discs.
A conventional spindle motor assembly used in disc drive applications is shown in FIG. 1. As seen therein, traditional spindle motor assemblies typically include a non-rotating spindle flange 100 that is securely fastenable to the drive housing. A rotatable spindle hub 106 is journaled about spindle flange 100, and is carried by an elongated rotatable shaft 112 that extends co-axially with the hub and flange. A pair of spaced apart ball bearings 115 are coupled between the shaft and flange to allow the spindle shaft 112 to rotate freely within the confines of spindle flange 100. A motor 118 is disposed directly underneath the spindle arrangement such that the motor components are located outside of the disc housing when the drive is assembled. The motor 118 includes a stator assembly 121 and a rotor assembly 124. The stator assembly includes a plurality of lamination stacks each having a winding wrapped thereabout. The rotor assembly 124 is attached to the spindle shaft by a lower hub 127. It includes a cup shaped rotor cap 130, a raised annular flange portion 132 with a plurality of magnets 133 disposed about the interior surface of the flange. Such an arrangement does not readily lend itself to miniaturization when used in conventional disc drives, since it has numerous components having large airspaces therein. Further, mere reduction in component size tends to weaken the component's structure, which tends to lead to faster wear and to lower the mechanical resonance frequencies of the motors. Such mechanical resonances generate acoustic noises which are irritating to users and therefore are preferably minimized.
One spindle motor design approach that has better space utilization than the traditional design incorporates an in-hub motor, as shown in FIG. 2. In this approach, a fixed shaft 150 is provided about which a spindle hub 152 is journaled. A pair of spaced-apart ball bearings 154, 155 are mounted directly between the fixed shaft and the rotatable hub 152. The rotor magnets 156 are carried directly by the spindle hub 152, and the stator windings 157 are disposed between the spaced apart ball bearings 154, 155. Although such a design is more compact than the traditional design described above, it suffers a drawback in that the bearings 154, 155 and the windings 157 compete for space within the hub region. This is not a particular problem in high profile disc drives, since there is ample room to provide sufficiently sized bearings and stator windings. However, in low profile disc drives, either the size (and strength) of the bearings or the size (and power) of the stator windings must suffer. Such a sacrifice is unacceptable for high quality, high performance disc drives.
Yet another recent approach is shown in FIG. 3. In this approach, a fixed shaft 170 is again used and the spindle hub 172 has a cup-shaped radial cross section. The bearings 174, 175 are placed between the shaft 170 and an inner wall 171 of the spindle hub 172. The hub has a large U-shaped trough 176 outside of the inner wall, and motor components are positioned within the enlarged trough 176. Specifically, the rotor magnets 178 are carried by an outer wall 179 of the spindle hub while the stator windings 181 are carried by a support ring 183 extending upward from the motor housing's base within the U-shaped trough. While such an arrangement allows adequately-sized bearings and stator windings, it requires a disc with a large inner diameter, since the hub must be quite large.
In view of the drawbacks of the prior art designs, there is a need for a compact spindle motor design that is capable of providing the performance required by state-of-the-art disc drives.